The present invention relates to drive mechanisms for sheet material feed arrangements. Specifically, the invention relates to improved antiskew roller assemblies for sheet material feed rollers suitable for use in imaging systems.
Imaging systems such as printers, fax machines, and copiers are virtually omnipresent, and can be found in homes and offices worldwide. The development of such systems has facilitated improvements in communication that have in turn fostered a sea change in the way people live and work. Telecommuting, paperless offices, and intra-office networks represent but a few examples of the advancements that have been made possible by modern imaging systems.
Since these systems have become crucial to everyday existence, their reliability and smooth operation is paramount. It is therefore vitally important to design imaging systems so that downtime and work interruptions are minimized. This can be a daunting challenge, given the relative complexity of systems in which sheet material must be infed, moved through the imaging process, and outfed in a matter of seconds.
One common and recurring problem in imaging systems is document misfeed, which can result in sheet material such as paper getting lodged in the transport mechanism. This condition, often referred to as a xe2x80x9cjamxe2x80x9d, is a source of frustration for system users.
One cause of such jams is xe2x80x9cskewxe2x80x9d, or misalignment of sheet material being transported through the imaging system. Skew can also cause other problems, such as marks on the sheet material and job misalignment.
The phenomenon of skew is illustrated in FIGS. 1 and 2. A sheet of material M, such as paper or transparency material, is transported through an imaging system by a set of transport rollers R. All points on the sheet M are moving at the same speed in the translational direction of the arrow A. As shown in FIG. 2, the rollers R are exerting uneven forces on the sheet M, causing a rotational movement is the direction of the arrow Axe2x80x2.
The causes of skew are best understood in the context of a typical idler roller arrangement, illustrated in FIGS. 3 and 4. A plurality of traction rollers T are mounted on a drive axle D. A corresponding plurality of idler rollers I are mounted in roller frames F. The roller frames F are pivotally mounted on a pivot axle P. The idler rollers I are urged against the traction rollers T by a plurality of springs S1 through S4, which are mounted on a rigid spring bar B.
The amount of spring strain produced by the springs S1 through S4 determines the amount of normal force applied to the traction rollers T by the idler rollers I. Since sheet material passes between the traction rollers T and the idler rollers I as it is transported through the imaging system, these normal forces also determine the amount and uniformity of translational movement applied to the sheet material. These forces are a function of the effective spring rates of the springs S1 through S4, which are determined by a variety of factors, for example, the mechanical properties and deformation of the individual springs, manufacturing processes used to produce the springs, and even the configuration of the roller frames and other housing geometry. If any of these factors differs from spring to spring, the normal forces exerted by the springs will be non-uniform. This condition frequently causes the rolling resistance on the sheet material to be greater on one side of the of the sheet than the other. The difference in rolling resistance imparts a rotational component to the movement of sheet material, thus causing skew.
It can thus be seen that the need exists for a simple, inexpensive mechanism to reduce the likelihood of skewing in sheet material transport systems.
These and other objects are achieved by providing an idler roller assembly in an imaging system including a sheet material transport roller system having drive rollers and idler rollers. The idler roller assembly includes a plurality of idler rollers. A plurality of springs are connected to apply respective normal forces to the idler rollers. Pivoting linkages are provided to equalize the normal forces applied to the respective rollers by respective springs.
In an embodiment, the plurality of idler rollers includes a first idler roller and a second idler roller. The plurality of springs includes a first spring connected to apply a normal force to the first idler roller and a second spring connected to apply a normal force to the second idler roller. The pivoting linkage includes a first pivoting lever member connected between the first spring and the second spring.
The first pivoting lever member can include a first end connected to the first spring member, and a second end connected to the second spring member. A fulcrum point is located between the first end and the second end of the first pivoting lever member.
The idler roller assembly can also be provided with a first spring bracket connecting the first end of the first pivoting lever member to the first spring member. A second spring bracket connects the second end of the first pivoting lever member to the second spring member.
The plurality of idler rollers can include a first idler roller, a second idler roller, a third idler roller, and a fourth idler roller. In such an embodiment, the plurality of springs includes a first spring connected to apply a normal force to the first idler roller, a second spring connected to apply a normal force to the second idler roller, a third spring connected to apply a normal force to the third idler roller, and a fourth spring connected to apply a normal force to the fourth idler roller. The pivoting linkage then includes a first pivoting lever member connected between the first spring and the second spring, a second pivoting lever member connected between the third spring and the fourth spring, and a third pivoting lever member connected between the first pivoting lever member and the second pivoting lever member.
The first pivoting lever member can include a first end connected to the first spring member, and a second end connected to the second spring member. A fulcrum point is located between the first end and the second end of the first pivoting lever member.
The second pivoting lever member includes a first end connected to the third spring member, and a second end connected to the fourth spring member. A fulcrum point is located between the first end and the second end of the second pivoting lever member.
The third pivoting lever member includes a first end connected to the fulcrum of the first pivoting lever member, and a second end connected to the fulcrum of the second pivoting lever member. A fulcrum point is located between the first end and the second end of the third pivoting lever member.
A method of reducing skew in sheet material transported by a roller system is also set forth. The method is described in the context of an imaging system including a sheet material transport roller system having at least one pair of drive rollers and at least one pair of corresponding idler rollers. In a first step, a respective spring is connected to each of the idler rollers in the at least one pair of idler rollers to apply respective normal forces to the idler rollers. A pivoting link is connected between the springs and the at least one pair of idler rollers to equalize the normal forces applied to the respective rollers by respective springs.
The features of the invention believed to be patentable are set forth with particularity in the appended claims. The invention itself, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings.